1. Field of the Invention
The invention relates generally to the use of automatic inspection of objects to perform three dimensional and two dimensional criteria analysis, and more specifically to the use of two and three dimensional criteria analysis to perform lead inspection, package mark and package inspection of integrated circuit devices including semiconductor circuits. The techniques and methods of the invention can also be applied to the inspection of solder balls of Ball Grid Array (BGA) integrated circuit packages and to the inspection of Chip Sized Packages (CSP) integrated circuit packages using computer vision.
2. Description of Related Art
This invention relates to combining two dimensional and three dimensional automated imaging inspection in a system. In the prior art, there are several approaches and some commercial applications which perform two dimensional (2D) and three dimensional (3D) image inspections individually. There are known systems which perform lead inspection (looking for and sometimes correcting bent leads), package mark inspection (checking the vendors mark and device number and type designators which are typically painted or printed on the plastic body of the package) and package defect inspection (holes, cracks or other irregularities in the surface of the plastic packaged device) of semiconductor packages. There also several known approaches relating to semiconductor package lead inspection of quad flat packages (hereinafter referred to as QFPs) and ball grid array packages (BGAs).
The following U.S. Patents are referred to herein as references typifying the approaches of the prior art.
______________________________________ 2d Mark Inspection 4,589,141 5/1986 Christian et al. 3d Lead Inspection 5,414,458 5/1995 Harris et al. 3d Thickness Inspection 3,671,726 6/1972 Kerr et al. 3d Information 4,259,589 3/1981 DiMatteo et al. 3d Sensors 4,891,772 1/1990 Case et al. 3d LaserProbe 4,733,969 3/1988 Case et al. 3d Imaging 5,024,529 6/1991 Svetkoff et al. 3d Triangulation 4,774,403 9/1988 Arts et al. ______________________________________
Several commercially available systems for inspecting integrated circuit packages are available. View Engineering provides systems where the image of a single point laser that oscillates at a high frequency, visible as a line on the object, is input into a camera. The laser points straight down from above the device undergoing inspection with the camera looking at an angle. The camera and laser source form the laser head. This laser head has to move over the entire device to generate a complete 3d image of the object. There are several problems with this approach . An X-Y positioner with a travel of greater than about 6".times.12" is required to move the laser head over a tray of devices. In addition, the X-Y positioner has to be attached to large granite blocks to dampen vibrations which could distort the results A separate camera performs a second inspection for package mark and package defects at a separate location on the machine.
In a system available from RVSI, Incorporated, a single point laser, with a one or more sensors, is used to triangulate to determine 3D inspection criteria. The laser sensors and the laser source form the laser head. This laser head is then moved over the device several times to generate 3D information of the points under the laser. The laser points straight down with the sensors at an angle to the laser.
Again, with the RVSI approach, an X-Y head positioner with a travel of greater than about 6".times.12" is required to move the laser head over a tray of devices. In addition, the X-Y positioner again has to be attached to large granite blocks to dampen vibrations. Package mark inspection and package defect inspection is performed by a separate camera placed at a separate location on the machine. For quad flat packages (QFPs), the package has to be placed so as have to be "live bug" (package normal orientation). However, for ball grid array packages (BGAs), these devices have to be placed "dead-bug" (upside down) for the inspection.
In systems available from ICOS, Incorporated, four light sources are used to form a shadow of the device leads. A single camera looks upwards to analyze the displacement of the shadow to determine 3D displacement of leads and so perform lead inspection. No laser light source is used. Again, there are several problems in this approach. As with the other systems, a separate camera inspects for package mark and package defects. The system cannot inspect BGA packages.
In systems currently available from Texas Instruments Incorporated, a single camera is used to look at the silhouette of the leads. The device is rotated four times to generate 4 images which is then analyzed to determine 3d displacement of leads. No laser light source is used. With this system, QFPs have to be positioned upside down and the system cannot inspect BGAs. Also, as with the other systems, a separate camera inspects for package mark and package defects.
Further with respect to the existing systems, most systems using triangulation to perform 3D criteria inspection have laser light sources going straight down at the object with the camera positioned at an angle of about 45 degrees. This implies modifying the plane of the CCD imager of the camera in order to achieve the Schiempflug condition of the optical axis of the lens, with the plane of the CCD imager and the plane of the laser source intersecting at a point. It is important to achieve this condition to have optimal focus of the object being looked at. This aspect of the prior art systems requires modifying a camera based on a CCD system.
Accordingly, a need thus exists for an apparatus and method for performing computer vision analysis of objects using a single camera solution to perform two-dimensional and three dimensional criteria analysis.